Lysine is an amino acid used extensively in the animal feed industry. The major form of L-Lysine used in the feed industry is L-LysineHCl (L-Lysine monohydrochloride). For many years, an L-LysineHCl solid has been produced by a process of fermentation, purification, crystallization and drying. After fermentation, the resulting broth may be rendered cell free by filtration or centrifugation. After filtration, the L-Lysine may be recovered from the fermentation broth by an ion exchange, which produces a liquid which is substantially L-Lysine free base. This solution may then be concentrated by evaporation.
Hydrochloric acid is usually added to the concentrated L-Lysine free base to form L-LysineHCl. This concentrated L-LysineHCl solution is crystallized to produce a product in the form of L-LysineHCl dihydrate (L-LysineHCl:2H.sub.2 O). This crystallized solid is thereafter dried to have less than one percent moisture.
This conventional product may have shortcomings. For example, it is dusty. During the handling of the product, the dust results in a loss of valuable material and sometimes causes an incomplete formulation. Also, human working conditions are made less healthful and more difficult by the dust contributed by the L-LysineHCl. Sometimes the product develops lumps during storage which are difficult to break up at the time of end use. In addition, the extensive use of ion exchange makes this process expensive. In particular, there is a need for a more economical process which avoids extensive ion exchange.
Direct spray drying of L-Lysine containing fermentation broth would avoid the extensive purification steps associated with the L-Lysine hydrochloride process, in particular the use of an expensive ion-exchange. However, consistent L-Lysine concentration in the final dry product would be difficult to achieve because the L-Lysine concentration in fermentation broth can vary considerably. Also, the product would b e dusty and difficult to use.
U.S. Pat. No. 5,431,933 describes a process for the production of an amino acid feed supplement which "still contains most of the solids content of the fermentation broth." The production of a fermentation broth at the industrial scale with 40 to 50 percent L-Lysine content is very difficult to achieve from an operational standpoint. Anyone skilled in the fermentation art is aware that upsets--contamination, power outages, operator error--are quite common and would likely produce material that was less than 40 to 50 percent L-Lysine and therefore unusable. This difficulty is compounded by the impurities associated with the media components, many of which are unrefined and vary in solids content and nutrient value from lot to lot. To avoid variance in media, fermentation would be constrained to specific and expensive media. These increases in operational input necessary to make a 40 to 50 percent L-Lysine product would cause the manufacturing costs to be prohibitive. In addition, the broth is dried to produce a powder. Powder is difficult to handle and can have detrimental health effects on workers due to dust inhalation. Thus, there is a need for an inexpensive process for the manufacture of a non-dusty L-Lysine product for use in feed supplements.
A process in which a non-dusty granular animal feed product is formed is described in U.S. Pat. No. 5,622,710. The granulation is accomplished in two steps. First, the fermentation broth is spray dried to produce particles of fermentation products and biomass. In the second step, the particles are converted into pellets by means of high shear mixing equipment. The additional step of using high shear mixing equipment to obtain a non-dusty product adds cost. Thus, there is a need for a process that leads to a non-dusty product which does not call for an expensive high shear mixing plant.
International Publication Number WO/95/23129 describes the production of non-stoichiometric salt of L-Lysine in granular form. This publication teaches the production of non-stoichiometric salts of L-Lysine wherein the amount of L-Lysine content in the final product is adjustable. While the requirement for hydrochloric acid is reduced, other materials are called for such as calcium hydroxide, sulfuric acid or phosphoric acid. In addition, the fermentation broth containing the L-Lysine is extensively ion-exchanged. Thus, there is a need for a more economical process to produce a granular product with an adjustable L-Lysine content which calls for fewer materials and which is not extensively ion exchanged.
U.S. Pat. No. 3,089,824 describes the use of a fluidized bed for the manufacture of compressed tablets for medical use. The process comprises (1) forming a suspension of particles in air, (2) enabling the particles to be built up with granulating material, and (3) coating the resulting granules with a lubricant. In one aspect of this invention, the granulating material is atomized and sprayed into the air stream of a fluidized bed of inert particles such as sucrose. The inert particles act as nuclei for the granulation process. The resulting granules are coated with a lubricant.